The NHANES is a stratified, multistage, probability cluster survey conducted in the noninstitutionalized U.S. population (8). Participants are interviewed in their home for basic demographic and health information. After the in-home interview, participants are scheduled to visit a mobile examination center (MEC) to complete physical examinations and laboratory measures (9,10). Between 1988 and 2010, the response rates for the interview ranged from 78.4 to 86.0%; for the examination, response rates ranged from 75.4 to 80.0%.

During 1988 to 2010, we found dramatic increases among diabetic individuals in the proportion who met ABC goals and who were taking statins. However, despite the strong scientific evidence showing the benefits of ABC control and statin use in reducing complications, many patients are not achieving ABC targets or taking statins. Almost half of Americans with diabetes did not meet each ABC goal, and 81.2% did not achieve all three goals.

Improvements in ABC control during the past 2 decades likely derive from new and improved therapeutic agents and increasing scientific evidence of risk factor control benefits that increased their use. Landmark studies in the 1990s, the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications, and the UK Prospective Diabetes Study (UKPDS), provided strong evidence that intensive glycemic therapy early in the course of type 1 and type 2 diabetes significantly reduced the risk of microvascular disease. Moreover, these microvascular disease benefits grew and CVD benefits emerged as participants continued to be monitored after the trials ended (2,13). In 1998, the Hypertension Optimal Treatment trial established the benefit of a diastolic BP goal <80 mmHg in reducing CVD in diabetes (14). Furthermore, in 1997, the Scandinavian Simvastatin Survival Study found that lipid control significantly reduced major CVD events among people with diabetes (15). Dissemination of knowledge from these pivotal studies (4), together with an increasing array of glycemic, antihypertensive, and lipid medications available for therapy, have made achievement of ADA goals more attainable, especially for those with less severe disease. In a national study of people with diabetes, self-reported use of antihypertensive medication significantly increased from 35% in 1999–2000 to 59% in 2007–2008; use of lipid medication significantly increased from 20 to 42% during the same period of time (16). The use of the oral diabetes medication metformin has steadily increased since U.S. Food and Drug Administration approval in 1995 and was the most frequent therapy in 2007 (54% of treatment visits) (17). Finally, with mainstream focus on the obesity and diabetes epidemics in the U.S. and increased attention to healthy behaviors, people may be more likely to seek care and physicians may be more vigilant about treating patients (18).

Few studies have assessed whether there are disparities by population subgroups in meeting ABC goals. The Look AHEAD (Action for Health in Diabetes) study, a randomized long-term weight loss trial in a selected population with diabetes, found that those who were older, white, and had a shorter duration of diabetes were more likely to meet the A1C goals; younger individuals and those not taking antihypertensive medication were more likely to meet BP goals; and older subjects, men, whites, those with longer disease duration, and those taking insulin, antihypertensive, or lipid medication were more likely to meet LDL goals (19). Results from Look AHEAD generally agree with our findings, and selected findings in the current study were replicated in a previous study using data from NHANES 1999–2006 (20). In addition, disparities in the prevalence of having A1C or BP levels greater than relaxed targets indicate subgroups in urgent need of additional treatment and care. Approximately 30% of younger adults, Hispanics, and those with ≥20 years of disease duration had an A1C ≥8.0% (≥64 mmol/mol); ∼40% of adults taking insulin or oral and insulin medication had an A1C ≥8.0% (≥64 mmol/mol); and approximately one-third of older adults, Hispanics, those with ≥20 years of disease duration, and those taking insulin had BP ≥140/90 mmHg. The disparities in ABC control highlight the need to address social determinants of poor control.

Suboptimal ABC control may be complicated by several factors. First, achieving ADA recommendations may be biologically unattainable for some patients due to severity of disease or other complications. Indeed, persons not taking any diabetes medications, having shorter time since diagnosis, and not having retinopathy, all of which are proxies for less advanced disease, were more likely to achieve A1C <7.0% (<53 mmol/mol). Glycemic control is more difficult in individuals with more severe β-cell loss. Notably, only 30% of those taking insulin achieved an A1C <7.0% (<53 mmol/mol), and more than one-third of this population did not achieve A1C <8.0% (<64 mmol/mol). Side effects of antihypertensives (electrolyte disturbances, renal dysfunction, orthostatic hypotension) and statins (musculoskeletal) may also limit their use and, therefore, the attainment of the treatment goals.

Second, individuals may lack self-management skills or the resources necessary for adherence to demanding self-care regimens, often involving polypharmacy, and lifestyle change. Previous studies suggest that people with diabetes are taking steps to improve lifestyle factors. Data from a national sample of overweight and obese subjects with diabetes indicated that the majority reported trying to lose weight (75%), increase physical activity (57%), and reduce the number of calories and fat in their diet (71%) (21). However, these lifestyle behaviors need to be sustained for measurable clinical improvements, and often, lifestyle behavior maintenance is challenging (22). Attaining ABC targets will require improved methods to increase adherence to prescribed medications, physical activity, healthy dietary choices, and access to support, including motivation and maintenance of behavior change.

Finally, because goals are increasingly being tailored on the basis of individual factors, it is not expected or desirable that everyone with diabetes should attain these targets. No information was available on medication compliance to further assess individualization of treatment.

It is noteworthy that we found younger people with diabetes were less likely to meet A1C and LDL goals and showed smaller improvements in meeting each ABC goal. However, the younger age group might have included more individuals with type 1 diabetes, which can be more difficult to control (23). In addition, survival bias may contribute to why older people have better control. Nevertheless, younger adults have more to gain from risk factor control because their life expectancy is longer and the potential for complications increases with the duration of diabetes. Thus, the ADA recommends more stringent A1C goals (<7.0%, <53 mmol/mol) for individuals with a longer life expectancy and shorter time since diagnosis and less stringent goals for those with longer time since diagnosis, established complications, or conditions limiting life expectancy (24). Not only did a much larger proportion achieve the less stringent A1C <8.0% (<64 mmol/mol; 77.9%) than A1C <7.0% (<53 mmol/mol; 52.5%) in 2007–2010, but the disparity in achieving these goals according to time since diagnosis was much less with a goal of A1C <8.0% (<64 mmol/mol) than the goal of A1C <7.0% (<53 mmol/mol). However, nearly 85% of adults aged >65 years achieved the less stringent A1C <8.0% (<64 mmol/mol) goal, but less than half of younger individuals achieved the more stringent goal of <7.0% (<53 mmol/mol) in 2007–2010. Moreover, whereas those without retinopathy and with shorter time since diagnosis were more likely to achieve an A1C <7.0% (<53 mmol/mol), nearly half of those without established CVD or retinopathy did not achieve this goal.

The greatest potential to reduce type 2 diabetes-related complications may lie in focusing on controlling A1C, BP, and LDL collectively. In the UKPDS, tight glycemic control alone in patients with newly diagnosed type 2 diabetes yielded a nonsignificant 16% decrease in CVD events and a significant 25% reduction in microvascular events (2). Those who lowered BP by 5 to 10 mmHg also significantly reduced their risk of stroke, diabetes-related death, heart failure, microvascular complications, and vision loss. In contrast, the Steno-2 Study, a randomized controlled trial among individuals with diabetes and microalbuminuria, tested a multifactorial intensive intervention targeting ABC control, aspirin therapy, diet, and physical activity. Hazard ratios were significantly reduced (0.41 for CVD events and 0.54 for overall mortality) in intensively treated participants compared with participants who received standard treatment from their general practitioner. The proportion of persons who met all three ABC goals (18.8%) was much lower than the proportion that met each individual ABC goal (51–56%). Thus, there may be a large opportunity to further reduce diabetes-related complications by focusing on the combined ABC goals, including lifestyle change as well as medication.

A strength of this study was the use of a nationally representative sample allowing generalization to the U.S. adult noninstitutionalized population. This analysis only reports ABC control for individuals who self-reported diabetes. Multiple clinical outcomes were assessed using standardized procedures, which allowed us to better characterize diabetes control. One limitation is that the small number of individuals in the fasting sample made some subgroup LDL estimates unreliable. Because participants taking insulin were not instructed to fast in NHANES 1988–1994, the estimates for meeting LDL goals in those years include few persons who were taking insulin. However, among those taking insulin, demographic characteristics and duration of diabetes were similar by fasting status. Nevertheless, the analysis of statin use did include individuals taking insulin and showed a higher proportion of statin use in insulin-treated individuals. There was a discrepancy between self-reported lipid medication use and documentation of statin use; this may have resulted because lipid medication use was only reported among those who were told by a physician to take medication because participants were unaware of their statin use and it was not reported or because prescription medication bottles were not brought to the MEC. Finally, a population-wide increase in A1C values was observed in the NHANES 2007–2010 study period compared with the 1999–2006 study period (25). After careful evaluation of the data, a cause for the shift could not be identified. The estimates for the 2007–2010 study period should be interpreted with consideration of these findings; the percentage achieving A1C <7.0% (<53 mmol/mol) may be underestimated in the current study.

Management of diabetes remains very complex and challenging, requiring access to a skilled team of clinicians and diabetes educators and imposing major burdens on families and health systems. Falling rates of amputation, end-stage renal disease, and death among those with diabetes attest to the effect of the improved control of the risk factors for complications we report here. The full effects of improved therapy for diabetes are often realized over decades. Thus, the steady improvement documented by our study portends further reductions in the proportion with complications among those with diabetes.

Yet, our data also show that there is much room for improvement. Access to care, education, and self-management support; personal knowledge, behavior, and adherence to therapy; healthy environments; as well as variation in the pathophysiology underlying diabetes all play important roles in achieving diabetes management goals that can improve long-term health of individuals with diabetes. Research is needed not only to identify optimal targets for therapy and provide information to tailor these targets based on individual factors but also to identify approaches to achieve these targets safely and efficiently. As the U.S. population ages and diabetes prevalence increases, it becomes increasingly urgent to find ways to overcome barriers to good diabetes management and deliver affordable, quality care so those with diabetes can live a longer and healthier life without serious diabetes complications.